Turbine rotor assembly

ABSTRACT

A turbine rotor assembly for extracting energy from an oscillating working fluid. The turbine rotor assembly includes a hub rotatable about a central axis. A plurality of blades is mounted to the hub about the central axis. Each blade has a leading edge and a trailing edge which are configured to be complementary in profile to each other such that the blades can be mounted in close fitting edge-to-edge proximity to each other.

FIELD OF THE INVENTION

The present invention relates generally to energy conversion devices.More particularly, this invention relates to turbines and primarily tounidirectional reaction turbines.

The invention has been developed primarily for use in an ocean waveenergy extraction system employing an oscillating water column and willbe described hereinafter with reference to this application. However, itwill be appreciated that the invention is not limited to this particularfield of use.

BACKGROUND OF THE INVENTION

With an ever increasing concern of the impact traditional energy systemshave had or are having on the environment, new methods and systems arecurrently being developed for reducing the impact such systems have onthe environment.

A number of these systems rely on turbines to rotate an electricgenerator in order to produce electricity. The problem with many suchsystems proposed to date is that a significant capital outlay isrequired to set up a new system. The extent of this capital outlay canoften act as a deterrent to investors, as the return on investment islimited to some extent by the relationship between the capital outlayand the efficiency of the system.

The turbines currently employed in such systems operate at a relativelow efficiency and the energy extraction system as a whole is limited bythe efficiency of these turbines.

It is an object of the present invention to overcome or ameliorate oneor more of the disadvantages of the prior art, or at least to provide auseful alternative.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided aturbine rotor assembly for extracting energy from an oscillating workingfluid, the turbine rotor assembly including:

a hub rotatable about a central axis;

a plurality of blades mountable to the hub about the central axis, eachblade having a leading edge and a trailing edge, wherein the leadingedge and trailing edge are configured to be complementary in profile toeach other such that the blades can be mounted in close fittingedge-to-edge proximity to each other.

Preferably, the plurality of blades are arranged sequentially to form acircular array about the central axis. The blades are preferablyarranged in a non-overlapping sequential formation.

It will be appreciated that the close fitting edge-to-edge proximitybetween sequentially mounted blades which can be achieved with thecomplementary profiled leading and trailing edges advantageously resultsin an increased frontal surface area of each blade, and consequentiallyreduces the gap between blades (when viewing the rotor from the front orback—i.e. along the line of the central axis). Moreover, thecomplementary profiles provide for a substantially constant gap widthalong the length of the adjacent edges. The gap is preferably as smallas possible and only provided for mechanical working clearances. Thatis, the width of the gap is preferably dictated by the predeterminedmechanical tolerances associated with manufacturing the blades. Incertain preferred embodiments, the gap width along the length ofadjacent blade edges is approximately 1 mm or less.

This increased surface area thus enables a working fluid to pass acrossmore blade surface which in turns improves the efficiency of the thrustarising from the lift forces generated by the working fluid flowing overthe blade and accelerating through the nozzle, the thrust acting torotate the hub and blades about the central axis.

Preferably, each blade is mounted to the hub via a mounting means. Themounting means preferably includes first mounting elements associatedwith the hub and second mounting elements associated with the blades,wherein each first mounting element cooperates with a respective one ofthe second mounting elements to securely mount the blade to the hub. Themounting means preferably includes a fastening means to engage and holdthe respective first and second mounting elements in fixed relation toeach other. The fastening means may, for example, be a fastener such asa screw or a screw and nut combination or the like.

In some preferred embodiments, each first mounting element is preferablyin the form of a plurality of receiving formations in the hub forreceiving the spindle or spigot of the associated blade. In certainpreferred embodiments, each second mounting element is a shaft, spindleor a spigot extending from a root of the blade.

Preferably, the blade is movable relative to the hub such that the bladecan change its pitch (or angle of attack) relative to the direction offlow of the working fluid so that the hub and blades rotate in the samedirection regardless of the fluid flow direction.

In some preferred embodiments, each blade moves in response to a forceor pressure applied to the blade by the working fluid. That is, eachblade is preferably configured to be self-rectifying such that itautomatically changes its pitch in response to the prevailingcharacteristics of the working fluid. For example, the blades may changetheir pitch in response to changes in pressure and/or direction of flowof the working fluid. In some embodiments, the mounting means isconfigured such that all blades change their pitch at the same time andby the same degree. In other preferred embodiments, the pitch of eachblade is changed independently to changes in pitch of the other blades.

Each blade is preferably rotatably mounted to the hub via a shaft,wherein the shaft or spindle defines an axis of rotation for that blade.Preferably, the shaft of each blade is mounted in a bearing arrangementin the associated receiving formation in the hub such that the blade isrotatable relative to the hub. The bearing arrangement preferablyincludes one or more bearings and may be a stacked arrangement of two ormore bearings. The stacked arrangement preferably includes a stack offour angular contact thrust ball bearings.

Each blade preferably rotates about its associated shaft/spindle tochange its pitch angle relative to the direction of flow of the workingfluid so that the hub and blades rotate in one direction only about thecentral axis. Preferably, each blade is configured to be able to rotateabout the spindle through a predetermined angle. In certain preferredembodiments, each blade can rotate through an angle of up toapproximately ±45°, ±40°, ±35°, ±30°, ±25°, ±20°, ±15°, ±10° or ±5°. Inone preferred embodiment, each blade can rotate through an angle of upto approximately ±16°. It will be appreciated that the actual anglethrough which the blade can rotate is not limited to the examplesprovided above, but rather can be configured to suit a particularapplication.

Preferably, the rotatable blades can be retained in a neutral positionor closed position wherein each blade is aligned around thecircumference of the hub to substantially or effectively close the fluidpassageway through the blades. The rotatable blades preferably can alsobe retained at the position of their maximum forward or reverse openingpositions to maintain an open passageway through the blades, the bladesmoving in either the forward or reverse opening direction depending onthe direction of fluid flow.

In some preferred embodiments, the blades are free to rotate in order tochange their pitch automatically in response to the changes to theprevailing working fluid and/or the pressure in the air chamber. Inother preferred embodiments, the changes to blade pitch are controlledby an actuator. The actuator is preferably responsive to changes in thecharacteristics/properties of the prevailing working fluid detected bysensors arranged within the flow passage (e.g. direction of flow and/orair chamber pressure). In various embodiments, the actuator can bemechanically, electromechanically, hydraulically or pneumaticallyoperated. Preferably, the actuator is configured to open the blades in afirst direction (e.g. forward direction upon exhaling of air from risingwave) based on upon a first set of criteria and in a second direction(e.g. reverse direction upon inhaling of air from a receding/fallingwave) based on a second set of criteria. The first and second sets ofcriteria preferably include different parameters.

In certain preferred embodiments, a control means is associated with theblades for controlling the changes in pitch. The control means ispreferably associated with the actuator of each blade. In some preferredembodiments, the controls means includes a damper or spring element forproviding a smooth and/or constant change in pitch. In otherembodiments, the control means can vary the speed at which the bladerotates. In certain embodiments, the control means can also act to limitthe degree or angle to which the pitch of the blade can change. Incertain preferred embodiments, the control means is in the form of areactive mechanical spring such as, for example, a leaf spring. Inothers forms, the control means includes a torque arm. In someembodiments, the actuator and/or control means are in communication witha central controller such as, for example, a programmable logiccontroller (PLC).

The leading edge and trailing edge of each blade is preferably curved orarcuate in shape. Preferably, each leading edge is convex in curvature.Preferably, each trailing edge is concave in curvature. In someembodiments, the curvature of the leading and trailing edges has aconstant radius of curvature. In other preferred embodiments, the radiusof curvature of the leading and trailing edges varies along the lengthof the respective edge. Preferably, the radius of curvature of theleading edge is greater than the radius of curvature of the trailingedge.

In other preferred forms, the leading and trailing edges of each bladeare substantially straight. In some embodiments, the straight edges ofeach blade taper away from each other from the root to the tip of theblade.

Preferably, the mounting means and shape of the blade is such that thecentre-of-pressure is operatively behind the axis of rotation of thespindle of each blade so that the blade is able to rotate about itsshaft in response to changes in pressure applied to the blade.

Preferably, each blade has a generally symmetrical cross-sectionalprofile. However, in certain preferred forms, asymmetric profiles can beemployed. The cross-sectional profile is preferably in the form of anaerofoil. Preferably, the aerofoil has a biconvex (or convex-convexo)profile. In other embodiments, one surface of the aerofoil has a concaveprofile and the opposing surface is convex. The aerofoil profilepreferably has an enlarged rounded leading edge and tapers inwardlytowards a narrower trailing edge. In other preferred forms, each bladehas a generally planar profile (e.g. a flat plate) with substantiallyparallel side faces.

In certain embodiments, the blades can be interchangeable with blades ofa different profile so as to achieve a different operatingcharacteristic of the turbine.

Preferably, the trailing edge of a first blade and the leading edge of asecond blade immediately following the first blade together define anozzle. It will be appreciated by those skilled in the art that thecomplementary shapes of the leading and trailing edges facilitate theprovision of a nozzle of substantially constant width when the bladesare in a neutral position or have a pitch angle of zero degrees (0°).

The control means preferably includes a pressure sensor for sensing thepressure in the air chamber of the oscillating water column (OWC) duct,the pressure sensor being operatively associated with the actuatorand/or control means such that when a predetermined pressure is sensedthe blades rotate to open the nozzles.

Preferably, each blade is in its closed position as the oscillatingwater column (OWC) starts to rise (i.e. at the OWC trough) such that theair passageway is effectively closed. The blades preferably open in afirst direction once a predetermined pressure has been reached in theair chamber. Preferably, the blades return to the closed position whenthe wave reaches its peak. As the wave starts to fall and with theblades in the closed position, a vacuum is preferably created in the airchamber. Preferably, the blades open in a second direction once apredetermined pressure has been reached in the air chamber. The bladespreferably open in the second direction once a predetermined negativepressure has been reached in the air chamber as the wave falls.

Preferably, the tip of each blade is curved. The tip of each blade ispreferably convex. Preferably, the curvature of the tip of each blade issuch that when the plurality of blades are mounted to the hub in acircular array the periphery of the array is generally in the form of acircle.

Preferably, the turbine rotor assembly is used in a single stageturbine. The turbine is preferably a unidirectional reaction turbine.However, the turbine rotor assembly could readily be adapted for use inmulti-stage turbines having two or more rotors.

The turbine rotor assembly is advantageously suited for use inextracting energy from an oscillating working fluid. More particularly,the turbine rotor assembly is suitable for use in an oscillating watercolumn (OWC) energy extraction system having an OWC duct. The rotorassembly is preferably mounted in the OWC duct of the energy extractionsystem such that an air chamber is defined within the duct between thesurface of the water in the duct and the hub and blades.

The rotor assembly is preferably adapted for rotation in a singledirection, independent of the direction of fluid flow. Preferably, therotor is arranged to be substantially normal to the direction of fluidflow with the axis of rotation substantially parallel to the fluiddirection.

The plurality of blades of the rotor assembly is preferably configuredsuch that the rotor rotates in a predetermined direction. Preferably,the rotor assembly is arranged substantially normal to the flowdirection of the working fluid such that it rotates about thelongitudinal axis of the housing. In other preferred forms, the rotorassembly is arranged to rotate in a direction substantially parallel tothe fluid flow direction.

Preferably, the turbine rotor assembly is rotatably arranged within aflow passage of a housing. The housing is preferably configured todirect the flowing working fluid towards the blades of the rotorassembly. In some embodiments, the housing is configured to have taperedor curved surfaces associated with the flow passage for directing theworking fluid towards the blades.

The housing is preferably longitudinal and extends along a longitudinalaxis. In some preferred embodiments, the housing has a generallycylindrical body. Preferably, the turbine rotor assembly is arrangedsubstantially coaxially with the longitudinal axis of the housing.

In certain embodiments, the housing is arranged such that itslongitudinal axis is arranged substantially parallel to the direction offlow of the oscillating working fluid. In other embodiments, the housingis arranged such that its longitudinal axis is arranged substantiallynormal to the direction of flow of the oscillating working fluid.

For example, in certain embodiments, the housing could be arranged suchthat the longitudinal axis is substantially vertical. In other preferredforms, the housing could be arranged such that the longitudinal axis issubstantially horizontal. It will be appreciated by those skilled in theart that the housing is not limited to those orientations describedabove, but could be arranged in any other suitable orientation, relativeto the direction of flow of the working fluid, to suit a particularapplication.

In certain embodiments, guide means is provided upstream of the rotorfor directing the working fluid towards the blades of the rotor.Preferably, the guide means includes first and second guides arranged onopposite sides of the rotor to direct the working fluid onto the bladesat a desired angle. In some embodiments, the guide means includes one ormore guide vanes arranged upstream of the rotor for directing theworking fluid towards the blades of the rotor. The guide vanes arepreferably arranged in a polar or circular array in proximity to theblades. The guide vanes may be associated with a stator or otherwisearranged within the housing. In certain embodiments, the guide meansincludes a nose cone extending from the hub.

It will of course be appreciated that the guide vanes are not limited toa particular form and therefore could be any suitable shape, includingcurved and planar shapes, for deviating the working fluid towards therotor blades.

The oscillating working fluid is preferably an oscillating airflow. Incertain preferred embodiments of the invention, the turbine rotor isconfigured for rotation by an airflow generated from an oscillatingwater column of an ocean wave energy extraction system, the oscillatingwater column (and thus the airflow) oscillating in response to the riseor fall of passing ocean waves.

It will, however, be appreciated by those skilled in the art that theoscillating working fluid is not limited to an oscillating airflow, andin particular, is not limited to an oscillating airflow produced from anoscillating water column. In certain embodiments, the turbine rotorassembly can be adapted for use with a unidirectional working fluid. Inembodiments adapted for unidirectional working fluids, the blades can bearranged in an overlapping formation wherein the leading and trailingedges of sequential blades overlap each other.

In preferred embodiments, the rotor has a drive shaft coupled at itsproximal end to the hub such that rotation of the hub causes acorresponding rotation of the drive shaft such that its distal end canbe used to engage and drive an electric generator.

The hub preferably has a mass which is sufficient for it to act as aflywheel to provide a substantially constant angular velocity, in use.

According to a second aspect of the invention, there is provided aturbine for extracting energy from an oscillating working fluid, theturbine including:

a housing; and

a turbine rotor assembly according to the first aspect of the invention,the turbine rotor assembly being rotatably mounted in the housing forunidirectional rotation in response to the oscillating working fluidflowing through the housing.

According to a third aspect of the invention, there is provided an oceanwave energy extraction system including:

a duct for receiving an oscillating water column, the oscillating watercolumn generating an oscillating airflow;

a housing connected to the duct to define a flow passage for theoscillating airflow;

a turbine rotor assembly according to the first aspect of the invention,the turbine rotor assembly being in fluid communication with theoscillating airflow such that the rotor is driven by the oscillatingairflow; and

an electric generator configured for rotation by the turbine rotorassembly to generate electrical energy.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a turbine rotor assembly according tothe invention;

FIG. 2 is a front view of the turbine rotor assembly of FIG. 1;

FIG. 3 is a side view of the turbine rotor assembly;

FIG. 4 is an enlarged view of the blades of the turbine rotor assembly;

FIG. 5 is a perspective view of a blade and spindle of the turbine rotorassembly;

FIG. 6 is a front view of the blade and spindle of FIG. 5;

FIG. 7 is a schematic illustration of a blade mounted to the hub;

FIG. 8 shows a pair of adjacent blades at three different pitch angle;

FIG. 9 shows the pressure profile across an aerofoil shaped blade and aplanar blade;

FIG. 10 shows three pairs of blades, each pair having a differentcross-sectional profile for various embodiments;

FIG. 11 shows a graph of the blade pitch angle against the height of theoscillating water column inside an OWC duct and against the pressurewith the air chamber between the water level and the rotor (hub andblade assembly); and

FIG. 12 shows a schematic diagram of an OWC energy extraction system inwhich the turbine rotor assembly is arranged.

PREFERRED EMBODIMENTS OF THE INVENTION

Referring to the drawings, the invention provides a turbine rotorassembly 1 for extracting energy from an oscillating working fluid inthe form of an oscillating airflow. The turbine rotor assembly 1 hasbeen developed specifically for use in an ocean wave energy extractionsystem (FIG. 12) of the type having an oscillating water column.

In such systems, the oscillating water column (OWC) is configured toproduce the oscillating airflow in response to the rise and fall ofpassing ocean waves. As the OWC rises in response to a passing wavecrest the OWC rises to produce an exhaust airflow. As the wave continuesand the following wave trough passes, the OWC falls to produce an intakeairflow.

With reference to FIG. 1, the turbine rotor assembly 1 includes a hub 2which is rotatable about its central axis 3. A plurality of blades 4 aremounted to the hub 2 about the central axis. As most clearly shown inFIG. 2, the blades are arranged in a non-overlapping, sequentialformation so as to form a circular array about the central axis 3 of thehub 2.

To mount the blades 4 on the hub 2, the hub has a series of firstmounting elements in the form of radial bores 5 circumferentiallyarranged about the periphery of the hub 2. Each blade 4 has a secondmounting element in the form of a spindle 6 which is received in anassociated bore 5 of the hub 2.

Each spindle 6 includes a bearing element 7 which enables the associatedblade 4 to be rotatable relative to the hub 2, about an axis of rotationdefined by the spindle 6. Each blade 4 is configured to be able torotate about its spindle 6 through a predetermined angle. In theillustrated embodiment, each blade 4 can rotate through an angle, forexample, approximately ±24°. In FIGS. 1 to 4, the blades 4 have rotatedto a position suitable for an exhaust airflow (flowing left-to-right inFIG. 3).

Each blade 4 moves in response to a force applied to the blade by theprevailing airflow fluid, the force arising from a pressure differenceacross the blades. The ability of the blades to change their pitch angleprovides the rotor 1 with a self-rectifying characteristic. Inparticular, the blades 4 can be rotated to suit either an intake or anexhaust airflow and maintain rotation of the hub 2 in a single directionabout its central axis.

A control means in the form of a reactive mechanical spring such as aleaf spring 8 is associated with each blade 4 for controlling thechanges to the pitch angle. The leaf spring 8 acts to provide a smoothand/or constant change in pitch. In addition, the leaf spring limits thedegree to which the pitch of the blade can change.

Referring now to FIGS. 5 and 6, each blade 4 has a leading edge 11 and atrailing edge 12. The leading and trailing edges (11, 12) areadvantageously configured to have complementary profiles to each othersuch that the blades 4 can be mounted to the hub 2 in close fittingedge-to-edge proximity to each other.

It will be appreciated by those skilled in the art that the closefitting edge-to-edge proximity between sequential blades, which can beachieved with the complementary profiled leading and trailing edges,advantageously results in an increased frontal surface area of eachblade, and consequentially reduces the gap between blades (when viewingthe rotor from the front or back—i.e. along the line of the centralaxis). Moreover, when the blades are in a neutral position (pitchangle=0°), the complementary profiles provide for a substantiallyconstant gap width along the length of the adjacent edges (11, 12).

In the neutral position, the gap between the blades is merely a clearlygap and minimised to the available manufacturing tolerances. As such,the total gap area is negligible and is sufficient to effectively closethe passageway and almost totally obstruct the flow of air through theblades. In other words, the solidity ratio (i.e. the ratio of the totalcombined blade area to the swept area of the blades) of the rotorassembly is almost 1.0. Accordingly, when the blades are in the neutralposition closing the passageway, the pressure in the air chamberincreases due to the decrease in volume as the wave rises. Similarly, asthe wave falls from its peak, the closed blades inhibit the intake ofair into the air chamber and thus allow the pressure in the chamber todrop.

The ability to hold the blades closed until a predetermined pressure isreached advantageously increases the magnification of the wave height inthe OWC duct to thereby improve the efficiency of the turbine. It hasbeen numerically modelled that an improvement in the total energyextraction can be achieved by holding the blades closed.

In addition, when the blades open, the increased surface area enablesthe airflow to pass across more blade surface which in turn providesadditional lift and thrust forces for rotating the hub and thus improvesthe efficiency of the rotor 1, as described in further detail below.This improved efficiency arises from an improved pressure profile acrosseach blade as shown in FIG. 9.

The substantially constant width of the gap defines a nozzle which, atleast in preferred forms, operates to increase the velocity of theprevailing airflow, further increasing the lift and thrust forcesapplied to the blades.

As most clearly shown in FIG. 7, the mounting means and shape of theblade is such that the centre-of-pressure (COP) is operatively behindthe axis of rotation of the spindle of each blade. That is, the leadingand trailing edges curve away from the spindle to place thecentre-of-pressure behind the axis of rotation to enable the blade torotate about the axis of rotation.

A variety of cross-sectional profiles of the blades are shown in FIGS.8, 9 and 10. With reference to these figures, it can be seen that eachblade preferably has a symmetrical cross-sectional profile.

The turbine rotor assembly 1 is rotatably arranged within a flow passageof a cylindrical housing 9. As most clearly shown in FIGS. 1 and 3, thehousing 9 is preferably configured to have curved inlet opening fordirecting the airflow towards the blades of the rotor. To furtherfacilitate directing of the airflow towards the blades, a nose cone 10extending from the hub 2 is provided.

In use, the hub 2 of the rotor 1 is preferably coupled to a drive shaftwhich is engaged to an electric generator (not shown). Rotation of thehub 2 causes a corresponding rotation of the drive shaft to drive theelectric generator.

The arrangement of the blades on the rotor assembly is such that in theneutral or non-actuated position, the fluid flow passage through thehousing is almost entirely blocked by the blades (albeit for the smallclearance gaps between sequential blades and between the tips of theblades and the housing). Such a blockage creates a full differentialpressure across the blades between the upstream and the downstream flowdirections. Computational fluid dynamic (CFD) analysis has shown that avery thin section blade yields excellent results and an aerofoil sectionshape is not critical.

This blockage of fluid flow establishes a pressure difference across theblades on the upstream and downstream sides of the blades. The pressuredifference creates a force normal to the surface of the blades with aresultant force comprising a component in the axial rotation directionof the rotor and a component in the direction of rotation of the rotor,this component being the torque that produces the power from theturbine. It will be appreciated that the terms “upstream” and“downstream” are used in a relative sense, dependent upon the directionof flow of the oscillating airflow.

In a power producing mode, the working fluid is allowed to pass betweenthe nozzles created between the leading and trailing edges of thesequentially arranged blades. The nozzles are created by a geometricrotation of the blades about an axis of rotation orthogonal, but notnecessarily perpendicular to, the axis of rotation of the central axisof the hub. The nozzles allow the working fluid to flow through thearray of blades in a preferred manner and rate such that the pressuredifferential across the upstream and downstream sides of the blade arrayis not substantially reduced compared to the pressure created when theblades are in their neutral position. That is, the pressure differenceacross the blades from the upstream to the downstream sides of theblades is advantageously substantially maintained when the nozzles arecreated by actuation of the blades from their neutral position.

The consequence of substantially maintaining the pressure differentialas the blades are rotated about their respective axes is a resultantrotation of the force vector acting across each blade such that theforce vector now contains an axial thrust component in the directionparallel to the central axis of rotation of the blade array and a thrustcomponent orthogonal to the central axis. This orthogonal thrustcomponent creates a torque moment on the hub which in turn producesuseful rotational power in the direction of rotation about the centralaxis of the rotor assembly.

The preferred method of forming each nozzle is by rotation of the entireblade about an axis orthogonal to the central axis of the hub. However,in other embodiments, the nozzles may be formed via the structuraldeformation of the blade. Such shape deformation may be via the appliedfluid pressure on the blade surface contributing to the deformation orvia other electromechanical induced control methods.

The configuration and profile of the nozzles can produce a secondarybenefit to the induced power producing thrust of the blades. Inparticular, the leading and trailing edges are preferably shaped todefine a nozzle profile with a smooth area reducing section to cause theflowing fluid to accelerate through the nozzle, thereby exchangingpressure energy for kinetic energy. The consequence of which is afurther reduction in pressure over the leading edge and forward sectionof the blades on the downstream side. This pressure reduction results ina normal force with a component in the axial and the rotationaldirections. The rotational direction force is converted to torque aboutthe central axis, whereby this extra contribution may further enhancethe magnitude of the rotational force vector.

The blade pitch angle and the corresponding pressure in the air chambercan be seen for a complete wave cycle in FIG. 11. It can be clearly seenfrom FIG. 11 that the blades are held closed when the blade is risingfrom its trough until a predetermined pressure is reached in thechamber. The blades are also held closed from the time the peak of thewave is reached until it falls and creates a second (negative)predetermined pressure in the chamber.

To hold the blades closed until a certain pressure in the chamber isachieved a mechanical spring system containing a spring pretension forceis used. In other forms, a hydraulic piston with a preload fluidpressure that is defined by the pressure in an accumulator or mechanicspring piston accumulator can be used. A magnetic actuator system with apreset holding force could also be used.

The closing of the blades includes a time dependent damping system suchthat the closing rate of the blades is reduced and blade closing ratebecomes independent of the pressure in the OWC (i.e. the damping systemacts against the spring pretension force). This system allows all of theair in the OWC chamber to escape at the end of the wave stroke. Thisallows for a greater internal wave height amplitude at the beginning ofthe next stroke as well as allowing more air to be entrained in thechamber before the up stroke and less air to be entrained in the chamberbefore the commencement of the down stroke.

The preset opening pressure is adjusted such that the preset openingpressure is a function of the rotational speed (rpm) of the turbine.This enhancement allows the turbine to operate in its optimal efficiencyrange as well as allowing the turbines rpm to more closely match theavailable wave energy states, specifically the height of the incomingwaves.

Advantageously, the inhale and exhale cycles of the turbine blade pitchcontrol can be independent from each other, as per the mechanismsdescribed above.

Again, the ability to control the blades such that they are held closeduntil a predetermined pressure is reached in the air chamber (for bothairflow directions) advantageously magnifies the amplification of theOWC and thereby increases the amount of pneumatic power extracted andimproves the efficiency of the turbine.

Accordingly, the present invention, at least in its preferredembodiments, provides a turbine rotor assembly of increased efficiency.The turbine rotor assembly advantageously enables increased amounts ofenergy to be extracted from an oscillating or bidirectional workingfluid. In particular, the turbine rotor assembly has blades whichadvantageously provide an increase frontal area of the turbine bladeswhich constricts the fluid flow passage to create a greater pressuredifferential across the blades, resulting in increases in the lift andthrust forces being applied to the blades. The close fittingedge-to-edge proximity of the blades also advantageously provides fornozzles which can increase the velocity of the airflow, again increasingthe pressure difference across the blade with a resultant increase inthrust.

The turbine rotor assembly is particularly suited for use in an oceanwave energy extraction system, wherein the working fluid is anoscillating airflow generated by an oscillating water column of theocean wave energy extraction system, the oscillating water column (andthus the airflow) oscillating in response to the rise of fall of passingocean waves.

In these and other respects, the invention in its preferred embodiments,represents a practical and commercially significant improvement over theprior art.

Although the invention has been described with reference to specificexamples, it will be appreciated by those skilled in the art that theinvention may be embodied in many other forms.

1. A turbine rotor assembly for extracting energy from an oscillatingworking fluid, the turbine rotor assembly including: a hub rotatableabout a central axis; a plurality of blades mountable to the hub aboutthe central axis, each blade having a leading edge and a trailing edge,wherein the leading edge and trailing edge are configured to becomplementary in profile to each other such that the blades can bemounted in close fitting edge-to-edge proximity to each other. 2.(canceled)
 3. A turbine rotor assembly according to claim 1, wherein theblades are arranged in a non-overlapping sequential formation.
 4. Aturbine rotor assembly according to claim 1, wherein each blade ismounted to the hub via a mounting means, wherein the mounting meansincludes a plurality of receiving formations in the hub and a shaftextending from a root of each blade, the shafts being receivable in thereceiving formations.
 5. (canceled)
 6. A turbine rotor assemblyaccording to claim 1, wherein the blade is movable relative to the hubsuch that the blade can change its pitch relative to the direction offlow of the working fluid.
 7. (canceled)
 8. A turbine rotor assemblyaccording to claim 6, wherein the mounting means is configured such thatall blades change their pitch at the same time and by the same degree.9. A turbine rotor assembly according to claim 6, wherein each bladerotates about its associated shaft to change its pitch angle relative tothe direction of flow of the working fluid so that the hub and bladesrotate in one direction only about the central axis, regardless of thedirection of fluid flow.
 10. (canceled)
 11. A turbine rotor assemblyaccording to claim 6, wherein the rotatable blades can be retained in aneutral position or closed position so that each blade is aligned aroundthe circumference of the hub to substantially close the fluid passagewaythrough the blades.
 12. A turbine rotor assembly according to claim 6,wherein the rotation of the blades is controlled by an actuator, theactuator being responsive to changes in the properties of the prevailingworking fluid within the flow passage.
 13. (canceled)
 14. A turbinerotor assembly according to claim 12, wherein, the actuator ismechanically, electromechanically, hydraulically or pneumaticallyoperated.
 15. A turbine rotor assembly according to claim 12, whereinthe actuator is configured to open the blades in a first direction basedon upon a first set of criteria and in a second direction based on asecond set of criteria, wherein the first set of criteria is determinedfrom properties associated with a rising wave and the second set ofcriteria is determined from properties associated with a falling wave.16. (canceled)
 17. A turbine rotor assembly according to claim 12,wherein a control means is in communication with the actuator forcontrolling movement of the blades.
 18. A turbine rotor assemblyaccording to claim 17, wherein the control means includes a damper forproviding a smooth and/or constant change in pitch.
 19. (canceled)
 20. Aturbine rotor assembly according to claim 1, wherein the leading edgeand trailing edge of each blade is curved or arcuate in shape. 21.(canceled)
 22. (canceled)
 23. A turbine rotor assembly according toclaim 6, wherein the leading and trailing edges of each blade aresubstantially straight.
 24. A turbine rotor assembly according to claim6, wherein the mounting means and shape of the blade is such that thecentre-of-pressure of the blade is operatively behind the axis ofrotation of the shaft of each blade.
 25. A turbine rotor assemblyaccording to claim 6, wherein each blade has a generally symmetricalcross-sectional profile.
 26. (canceled)
 27. (canceled)
 28. (canceled)29. A turbine rotor assembly according to claim 6, wherein the trailingedge of a first blade and the leading edge of a second blade immediatelyfollowing the first blade together define a nozzle.
 30. A turbine rotorassembly according to claim 29, including a pressure sensor for sensingthe pressure in an air chamber of an oscillating water column duct inwhich the hub and blades are arranged, the pressure sensor beingoperatively associated with the actuator and/or control means such thatwhen a predetermined pressure is sensed the blades rotate to open thenozzles.
 31. A turbine rotor assembly according to claim 1, wherein theturbine rotor assembly is rotatably arranged within a flow passage of ahousing, wherein the housing is configured to direct the flowing workingfluid towards the blades of the hub and blade assembly.
 32. (canceled)33. (canceled)
 34. (canceled)
 35. A turbine rotor assembly according toclaim 1, wherein a drive shaft is coupled to the hub at its proximal endand to an electric generator at its distal end.
 36. (canceled) 37.(canceled)
 38. (canceled)